This invention relates to a drive coupling bushing assembly for marine propellers. The drive train for marine propulsion equipment presently marketed typically includes a coupling employing an annular rubber bushing element between inner and outer sleeves, one of which rotates the bushing and the other of which is rotated by the bushing. Such a drive coupling employs a frictional drive engagement between the bushing and the outer sleeve, enabling controlled slippage in the event the propeller strikes an object. Assembly of these components is typically achieved by bonding the rubber bushing element to the inner sleeve as by vulcanizing and/or use of polymeric bonding agents, and press fitting the bushing element into the outer sleeve. A general assembly of this type for an inboard-outboard arrangement is set forth in U.S. Pat. No. 3,146,612. It will be appreciated that slippage at this bushing therefore occurs only under special circumstances, as a safety factor.
More recently the increased power output of marine engines and the increase in propeller effectiveness has resulted in unwanted slippage in the conventional bushing assembly when power is rapidly applied from the engine to the drive shaft to the propeller. This slippage of course prevents the power from being fully applied to the propeller. Moreover, repeated slippage of the bushing significantly lessens its frictional engagement, leading to steadily decreasing effectiveness and ultimate failure.